What is Polyacrylamide?

Polyacrylamide, or PAM, is an organic polymer formed from acrylamide sub-units. Initially, it is produced with a simple, repeating, linear chain structure, but can be modified to form highly structured, branched and cross-linked variants.

It has many uses throughout a wide range of industrial processes, but one of the main purposes is in the separation of solids/liquids in the municipal and industrial waste water sectors.

As part of the manufacturing process, the ionic characteristics of the polymer can be manipulated to achieve varying degrees of anionic (negative charge) or cationic (positive charge) qualities and non-ionic (minimal charge), which is a key factor during the polymer selection process.

The nature of the sludge/effluent to be treated is the driving force behind the initial charge selection (positive or negative) and the individual characteristics of the sludge determine the ionic charge required (high or low cationicity/anionicity). As a basic rule of thumb, municipal waste (primary sludge, SAS and digested sludge) requires a cationic polymer system and industrial effluents (tanneries, aggregate washing and metal finishing) require an anionic treatment.

HOWEVER, THERE ARE EXCEPTIONS TO THIS RULE AND ASSUMPTIONS SHOULD NOT BE MADE!

Polymers, both anionic and cationic, work by a process called flocculation. A required polymer is made into a solution with potable water in a suitable blending tank or vessel at the desired concentration and this is added to the colloidal matrix. As the polymer solution mixes with the effluent, it binds the small particulates together to form larger masses, or flocs, which then readily precipitate out of the solution by gravity to leave a clear supernatant. This thickened material can then be processed via a dewatering system, such as a centrifuge, to produce a ‘de-watered’, dry cake which is easier/cheaper to transport and dispose of by the desired method.

By using a polymer treatment, companies can achieve much faster separation of solids/liquids allowing greater throughput of treated effluent and to meet the requirements of local authorities, such as quality of the supernatant/waste water prior to discharge to sewers or other water courses.

The molecular weight, or length of chain, of the polymer also plays a part in product selection. The higher the molecular weight, the more viscous the polymer solution and the better the shear resistance – critical for applications such as centrifuges where strong mixing forces can cause low molecular weight polymers to break down and become ineffective.

SNF is the world’s leading polyacrylamide manufacturer, supplying a range of flocculants and coagulants for Industrial & Municipal Wastewater treatment and can be supplied in powder, emulsion or block forms depending on the type of make-up kit available or customer preferences.